diff --git a/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualDirectory.java b/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualDirectory.java
index 69a76b39a..6e808a180 100644
--- a/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualDirectory.java
+++ b/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualDirectory.java
@@ -15,8 +15,6 @@
  */
 package org.teavm.classlib.fs;
 
-import java.io.InputStream;
-import java.io.OutputStream;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
@@ -48,12 +46,7 @@ public class InMemoryVirtualDirectory extends AbstractInMemoryVirtualFile {
     }
 
     @Override
-    public InputStream read() {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public OutputStream write(boolean append) {
+    public VirtualFileAccessor createAccessor() {
         throw new UnsupportedOperationException();
     }
 
diff --git a/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualFile.java b/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualFile.java
index 666f04554..e29139f69 100644
--- a/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualFile.java
+++ b/classlib/src/main/java/org/teavm/classlib/fs/InMemoryVirtualFile.java
@@ -15,10 +15,7 @@
  */
 package org.teavm.classlib.fs;
 
-import java.io.ByteArrayInputStream;
 import java.io.IOException;
-import java.io.InputStream;
-import java.io.OutputStream;
 import java.util.Arrays;
 
 public class InMemoryVirtualFile extends AbstractInMemoryVirtualFile {
@@ -50,23 +47,37 @@ public class InMemoryVirtualFile extends AbstractInMemoryVirtualFile {
     }
 
     @Override
-    public InputStream read() {
+    public VirtualFileAccessor createAccessor() {
         if (parent == null) {
             return null;
         }
-        return new ByteArrayInputStream(data, 0, size);
-    }
 
-    @Override
-    public OutputStream write(boolean append) {
-        if (parent == null) {
-            return null;
-        }
-        if (!append) {
-            data = new byte[0];
-            size = 0;
-        }
-        return new OutputStreamImpl(data, size);
+        return new VirtualFileAccessor() {
+            @Override
+            public int read(int pos, byte[] buffer, int offset, int limit) throws IOException {
+                limit = Math.max(0, Math.min(size - pos, limit));
+                System.arraycopy(data, pos, buffer, offset, limit);
+                return limit;
+            }
+
+            @Override
+            public void write(int pos, byte[] buffer, int offset, int limit) throws IOException {
+                expandData(pos + limit);
+                System.arraycopy(buffer, offset, data, pos, limit);
+                size = pos + limit;
+            }
+
+            @Override
+            public int size() {
+                return size;
+            }
+
+            @Override
+            public void resize(int size) throws IOException {
+                expandData(size);
+                InMemoryVirtualFile.this.size = size;
+            }
+        };
     }
 
     @Override
@@ -84,73 +95,10 @@ public class InMemoryVirtualFile extends AbstractInMemoryVirtualFile {
         return size;
     }
 
-    class OutputStreamImpl extends OutputStream {
-        byte[] data;
-        int pos;
-
-        OutputStreamImpl(byte[] data, int pos) {
-            this.data = data;
-            this.pos = pos;
-        }
-
-        private void ensureIO() throws IOException {
-            if (data == null) {
-                throw new IOException("Stream was closed");
-            }
-        }
-
-        @Override
-        public void write(int b) throws IOException {
-            ensureIO();
-            expandData(pos + 1);
-            data[pos++] = (byte) b;
-            sync();
-        }
-
-        private void expandData(int newSize) {
-            if (newSize > data.length) {
-                int newCapacity = Math.max(newSize, data.length) * 3 / 2;
-                boolean actual = data == InMemoryVirtualFile.this.data;
-                data = Arrays.copyOf(data, newCapacity);
-                if (actual) {
-                    InMemoryVirtualFile.this.data = data;
-                }
-            }
-        }
-
-        private void sync() {
-            if (data == InMemoryVirtualFile.this.data) {
-                size = pos;
-                modify();
-            }
-        }
-
-        @Override
-        public void write(byte[] b, int off, int len) throws IOException {
-            ensureIO();
-            if (len == 0) {
-                return;
-            }
-
-            if (off < 0 || len < 0 || off + len >= b.length) {
-                throw new IndexOutOfBoundsException();
-            }
-
-            expandData(pos + len);
-            while (len-- > 0) {
-                data[pos++] = b[off++];
-            }
-
-            sync();
-        }
-
-        @Override
-        public void close() throws IOException {
-            data = null;
-        }
-
-        @Override
-        public void flush() throws IOException {
+    private void expandData(int newSize) {
+        if (newSize > data.length) {
+            int newCapacity = Math.max(newSize, data.length) * 3 / 2;
+            data = Arrays.copyOf(data, newCapacity);
         }
     }
 }
diff --git a/classlib/src/main/java/org/teavm/classlib/fs/VirtualFile.java b/classlib/src/main/java/org/teavm/classlib/fs/VirtualFile.java
index ce838eee4..6a214c5bc 100644
--- a/classlib/src/main/java/org/teavm/classlib/fs/VirtualFile.java
+++ b/classlib/src/main/java/org/teavm/classlib/fs/VirtualFile.java
@@ -15,9 +15,6 @@
  */
 package org.teavm.classlib.fs;
 
-import java.io.InputStream;
-import java.io.OutputStream;
-
 public interface VirtualFile {
     String getName();
 
@@ -29,9 +26,7 @@ public interface VirtualFile {
 
     VirtualFile getChildFile(String fileName);
 
-    InputStream read();
-
-    OutputStream write(boolean append);
+    VirtualFileAccessor createAccessor();
 
     VirtualFile createFile(String fileName);
 
diff --git a/classlib/src/main/java/org/teavm/classlib/fs/VirtualFileAccessor.java b/classlib/src/main/java/org/teavm/classlib/fs/VirtualFileAccessor.java
new file mode 100644
index 000000000..79ab0c2a3
--- /dev/null
+++ b/classlib/src/main/java/org/teavm/classlib/fs/VirtualFileAccessor.java
@@ -0,0 +1,28 @@
+/*
+ *  Copyright 2017 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.classlib.fs;
+
+import java.io.IOException;
+
+public interface VirtualFileAccessor {
+    int read(int pos, byte[] buffer, int offset, int limit) throws IOException;
+
+    void write(int pos, byte[] buffer, int offset, int limit) throws IOException;
+
+    int size();
+
+    void resize(int size) throws IOException;
+}
diff --git a/classlib/src/main/java/org/teavm/classlib/java/io/TFile.java b/classlib/src/main/java/org/teavm/classlib/java/io/TFile.java
index 7910b020f..92fdb7e1d 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/io/TFile.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/io/TFile.java
@@ -366,6 +366,11 @@ public class TFile implements Serializable, Comparable<TFile> {
         return path.hashCode();
     }
 
+    @Override
+    public String toString() {
+        return path;
+    }
+
     private static String fixSlashes(String origPath) {
         int uncIndex = 0;
         int length = origPath.length();
diff --git a/classlib/src/main/java/org/teavm/classlib/java/io/TFileInputStream.java b/classlib/src/main/java/org/teavm/classlib/java/io/TFileInputStream.java
index 62d7ff407..117a1504c 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/io/TFileInputStream.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/io/TFileInputStream.java
@@ -18,10 +18,14 @@ package org.teavm.classlib.java.io;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.Objects;
 import org.teavm.classlib.fs.VirtualFile;
+import org.teavm.classlib.fs.VirtualFileAccessor;
 
 public class TFileInputStream extends InputStream {
-    private InputStream underlyingStream;
+    private VirtualFileAccessor accessor;
+    private int pos;
+    private boolean eof;
 
     public TFileInputStream(TFile file) throws FileNotFoundException {
         VirtualFile virtualFile = file.findVirtualFile();
@@ -29,39 +33,78 @@ public class TFileInputStream extends InputStream {
             throw new FileNotFoundException();
         }
 
-        underlyingStream = virtualFile.read();
-        if (underlyingStream == null) {
+        accessor = virtualFile.createAccessor();
+        if (accessor == null) {
             throw new FileNotFoundException();
         }
     }
 
-    @Override
-    public int read(byte[] b) throws IOException {
-        return underlyingStream.read(b);
-    }
-
     @Override
     public int read(byte[] b, int off, int len) throws IOException {
-        return underlyingStream.read(b, off, len);
+        Objects.requireNonNull(b);
+        if (off < 0 || len < 0 || off + len > b.length) {
+            throw new IndexOutOfBoundsException();
+        }
+        if (eof) {
+            return -1;
+        }
+        ensureOpened();
+        int result = accessor.read(pos, b, off, len);
+        pos += result;
+        if (pos == accessor.size()) {
+            eof = true;
+        }
+        return result;
     }
 
     @Override
     public long skip(long n) throws IOException {
-        return underlyingStream.skip(n);
+        ensureOpened();
+        if (eof) {
+            return 0;
+        }
+        int newPos = Math.max(pos, Math.min(accessor.size(), pos));
+        int result = newPos - pos;
+        pos = newPos;
+        if (result == 0) {
+            accessor = null;
+        }
+        return result;
     }
 
     @Override
     public int available() throws IOException {
-        return underlyingStream.available();
+        ensureOpened();
+        if (eof) {
+            return 0;
+        }
+        return Math.max(0, accessor.size() - pos);
     }
 
     @Override
     public void close() throws IOException {
-        underlyingStream.close();
+        accessor = null;
     }
 
     @Override
     public int read() throws IOException {
-        return underlyingStream.read();
+        ensureOpened();
+        if (eof) {
+            return -1;
+        }
+        byte[] buffer = new byte[1];
+        int read = accessor.read(pos, buffer, 0, 1);
+        if (read == 0) {
+            eof = true;
+        } else {
+            pos++;
+        }
+        return !eof ? buffer[0] : -1;
+    }
+
+    private void ensureOpened() throws IOException {
+        if (accessor == null) {
+            throw new IOException("This stream is already closed");
+        }
     }
 }
diff --git a/classlib/src/main/java/org/teavm/classlib/java/io/TFileOutputStream.java b/classlib/src/main/java/org/teavm/classlib/java/io/TFileOutputStream.java
index c50650711..13c4f5909 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/io/TFileOutputStream.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/io/TFileOutputStream.java
@@ -19,10 +19,13 @@ package org.teavm.classlib.java.io;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.OutputStream;
+import java.util.Objects;
 import org.teavm.classlib.fs.VirtualFile;
+import org.teavm.classlib.fs.VirtualFileAccessor;
 
 public class TFileOutputStream extends OutputStream {
-    private OutputStream underlyingStream;
+    private VirtualFileAccessor accessor;
+    private int pos;
 
     public TFileOutputStream(TFile file) throws FileNotFoundException {
         this(file, false);
@@ -40,34 +43,47 @@ public class TFileOutputStream extends OutputStream {
             throw new FileNotFoundException();
         }
 
-        underlyingStream = virtualFile.write(append);
-        if (underlyingStream == null) {
+        accessor = virtualFile.createAccessor();
+        if (accessor == null) {
             throw new FileNotFoundException();
         }
+
+        if (append) {
+            pos = accessor.size();
+        }
     }
 
-    @Override
-    public void write(byte[] b) throws IOException {
-        underlyingStream.write(b);
-    }
-
     @Override
     public void write(byte[] b, int off, int len) throws IOException {
-        underlyingStream.write(b, off, len);
+        Objects.requireNonNull(b);
+        if (off < 0 || len < 0 || off + len > b.length) {
+            throw new IndexOutOfBoundsException();
+        }
+        ensureOpened();
+        accessor.write(pos, b, off, len);
+        pos += len;
     }
 
     @Override
     public void flush() throws IOException {
-        underlyingStream.flush();
     }
 
     @Override
     public void close() throws IOException {
-        underlyingStream.close();
+        accessor = null;
     }
 
     @Override
     public void write(int b) throws IOException {
-        underlyingStream.write(b);
+        ensureOpened();
+        byte[] buffer = { (byte) b };
+        accessor.write(pos, buffer, 0, 1);
+        pos++;
+    }
+
+    private void ensureOpened() throws IOException {
+        if (accessor == null) {
+            throw new IOException("This stream is already closed");
+        }
     }
 }